1. Field of the Invention
This invention relates to a rupture disc of frangible material disposed between separate propellant chambers of a multi-stage missile, wherein a central portion of the frangible disc has an aperture for receiving an igniter and is circumscribed by a line of weakness to enable the central portion and the igniter to remain in fixed disposition as a plurality of sector-shaped segments surrounding the central portion simultaneously rupture when subjected to burst pressures and move outwardly for timed release of the next stage of propellants.
2. Description of the Prior Art
Missiles having motors that sequentially release separate stages of propellant are known to provide greater accuracy of control over the speed and destination of the missile then would be possible using, for instance, a single stage motor having propellants that burn on a continuous basis. For example, a first stage of a two-stage missile could be ignited for overcoming gravitational forces and initially launching the missile, and subsequently a second stage of solid propellant could be utilized to propell the missile to the target once the launch is complete. Multi-stage missiles can optionally use different propellants in each stage to further improve dynamic control of movement and thrust.
Rupture discs provide separation of propellants in adjacent fuel chambers of a multi-stage missile to enable to propellant in the stages to be ignited and released in a pulsed or sequential order. The rupture discs are typically pre-bulged and formed to complementally engage a backup support member disposed toward the upstream stage so that the disc will not collapse under the relatively large pressures that are generated during burning of the downstream stage. The backup support has internal passageways for enabling venting of the upstream stage once the latter is ignited and the rupture disc bursts. Moreover, the rupture disc can be provided with an insulating material such as synthetic rubber to prevent the disc from being subject to heat-related damage during combustion of propellants in the downstream stage.
As can be appreciated, the operating characteristics of a rupture disc assembly which separates adjacent stages of a solid propellant missile must meet stringent criteria to ensure satisfactory performance of the missile. The rupture disc assembly must completely isolate adjacent propellant chambers and must not fracture, crack or otherwise leak when subjected to the relatively large back pressures generated during burning of the propellant in the first stage, since such leakage might prematurely detonate the second or upstream stage. On the other hand, once ignition of the second stage is desired, it is important that the rupture disc move quickly out of the pathway of the escaping propellants and not fracture into small fragments that might otherwise become lodged in a position to obstruct the flow of materials from the second stage, since any flow obstruction might cause an explosion of the missile.
In the past, certain missile bulkhead rupture discs have been provided with radially extending, scored lines of weakness to facilitate rupturing of the disc in such a manner that a plurality of sector-shaped petals rupture and move outwardly toward the missile casing. In such missiles, wires from an electronic control apparatus which lead to an electric igniter for the first or downstream stage of propellants are secured to the missile casing and extend around the outside of the rupture disc. However, such an arrangement creates numerous difficulties, particularly in sealing the second stage from leakage of pressurized combustants in a path from the first stage along the area when the wires extend around the rupture disc, and hence a multitude of carefully prepared seals and welds are required in an effort to prevent such leakage. Moreover, use of two-part, modular casings is not possible in this type of construction, due to the complex seals and welds that must be provided to prevent leakage between the stages.